Anti-static treatment for photographic products on polyethylene coated paper



y 1966 FRANKLIN Y. CHU ETAL 3,253,922

ANTI-STATIC TREATMENT FOR PHOTOGRAPHIC PRODUCTS ON POLYETHYLENE COATED PAPER Filed Sept. 18, 1961 FRANKLIN CHU FRANK B. SPELBR/NK INVENTOR5 BY @MM WNMJJQ ATTORNEY AGENT United States Patent ANTI-STATIC TREATMENT FOR PHOTOGRAPHHC PRUDUCTS 0N PGLYETHYLENE COATED PAPER Franklin Y. Chu and Frank B. Spelblink, both of Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N .Y., a corporation of New Jersey Filed Sept. 18, 1961, Ser. No. 138,556 7 Claims. (Cl. 96-85) This invention concerns polymeric coated photographic paper, more particularly polyethylene coated paper,

which has been treated to reduce the formation of static charges.

Static charges have caused considerable trouble by causing static markings on sensitized photographic products. These charges may be produced by the friction of photographic products moving over rollers by the separation of emulsion from the backing side of paper upon the unrolling of a large roll of paper. When the static is discharged, the discharge is manifested as irregular fog patterns in the emulsion after it has been developed.

Attempts have been made to overcome the problem of static electricity in photographic paper by the application of various layers to the paper base. These layers have in general consisted of materials designed to dissipate the electric charges by providing the paper with a conducting surface. Materials which absorb moisture and therefore provide a conducting surface have frequently been employed.

The problem of static electricity has not been as serious With photographic paper as with photographic film, but the advent of polymeric coatingson photographic paper such as polyethylene resulted in the necessity for finding means of solving the problems of static charges on these photographic elements. A conventional method of antistatic treatment has been to apply a continuous layer of conductive material on one or both surfaces of the polyethylene. However, this has presented problems in itself due to the inherent nature of the polyethylene surface which is hydrophobic and resists adhesion to coatings in general. This requires a separate treatment of the polyethylene surface such as electron bombardment, subcoatings or the like, treatments which are required before the antistatic coating can be added. Moreover, these antistatic coatings have the possibility of interfering with subsequent coatings on the polyethylene surface due to physical transfer, repellency, or chemical or photographic activity. In addition, they were subject to being disturbed due to rubbing the surface of the polyethylene, passage over handling means of various types and the like.

We have found that antistatic agents can be added to the paper itself prior to being coated with the polymeric coating such as polyethylene and that the antistatic character of the paper is improved so that it can be suitably used for photographic purposes.

One object of this invention is to provide an antistatic treatment for photographic paper having a coating of polyethylene. A further object is to provide a method of treating photographic paper so that it can be subsequently coated with a synthetic organic thermoplastic coating and which will be resistant to the accumulation of static charges. An additional object is to provide a photographic paper which has an antistatic treatment thereon which will not interfere with the sensitivity, or the like, of the subsequently coated silver halide emulsion.

The above objects are obtained by incorporating the antistatic agent in the photographic paper either by coating it on the paper base itself or by incorporating it into 3,253,922 Patented May 3 1, 1966 the paper tub sizing solutions while the paper is being made. The paper so treated is then coated with a thermoplastic resin such as polyethylene or the like on one or both sides forming a barrier between the antistatic coating and the photographic emulsion but at the same time providing antistatic characteristics for the photographic paper. The choice of whether one or both sides of the paper is coated with polyethylene depends on the purpose for which the paper is intended and also on the possible photographic activity of the antistatic coating. For instance, if an antistatic agent is used which has a photographic action, it is desirable to coat the paper on both sides with polyethylene.

Polyethylene coated paper having the antistatic treatment on the paper base may be subsequently treated to obtain adhesion of the photographic emulsion. The method known in the art for treating the polyethylene surface may advantageously be used without in any way affecting the antistatic properties of the paper. These methods include electron bombardment, flame treatment, oxidation using sulfuric acid-bichromate solution, peroxides and the like, subbing using colloidal silica, colloidal zioconia, or incorporating silica of larger than colloidal size in the polyethylene surface. Other methods than those already disclosed may be used.

The antistatic agent used in our preferred embodiment is the sodium salt of naphthalene sulfonic acid which may be coated from an aqueous solution. However, a great number of known antistatic agents may be used and these are intended to be within the scope of our invention. These may include various salts, such simple salts as sodium sulfate and the like salts of organic compounds, such as the alkali metal and ammonium salts of the condensation products of an aldehyde such as formaldehyde with naphthalene sulfonic acids; organic antistatic agents, such as triethanolamine oleate, triethanolamine stearate, and various polyalkylene polyamine derivatives. Oxyalkylene amine derivatives of phosphorous, polyacrylyoxyalkyl trialkyl ammonium alkylsulfate salts, diethanolamine salts of phosphate esters, and the like may also be used. When the polyethylene or thermoplastic coating is on only one side, it will be clear that the materials which rely on their ability to absorb moisture may also be operative. These include such materials as hydroxy ethers, polyhydroxy alcohols, and the like.

The coating range of the thermoplastic material may range as high as 2.0 mil in thickness. However, our preferred range is 0.4-0.6 mil of polyethylene or other organic thermoplastic material.

In addition to the various coating and antistatic compounds which are commonly known for the purpose of reducing static charges, materials may be incorporated into the paper base itself such as. carbon to provide conductivity through the paper. It seems clear that the more conductive the antistatic agent, as measured by surface and/ or volume resistance measurements of the paper base, the greater the static protection. Therefore, there is no restriction to any one class of compound with regard to the particular antistatic agent which may be used.

The antistatic agent may be incorporated in various means, so that the solvent if one is required is not important. The electrical characteristics of the final dried down material are the important criteria of operatability. Aqueous solutions are generally preferred because of the ease of adapting them to manufacturing operations. However, this does not rule out organic solvents or hot melt coatings.

The amount of electrostatic agent incorporated in the paper depends on the type of antistatic agent. For instance, the sodium salt of naphthalene sulfonic acid can be surface coated in an 8.5% aqueous solution to give a resulting content of 0.6l.5 pounds per 1000 sq. ft. of paper stock which is adequate when the paper is subsequently overcoated with polyethylene films on both sides.

Accordingly, the amount of antistatic agent is described EXAMPLE 1 An 8.5% aqueous solution of a sodium salt of naphthalene sulfonic acid was surface coated on a 25-lb. per 1000 sq. ft. paper stock to obtain a coverage of 0.6 pounds per 1000 sq. -ft. and a resulting surface resistance of 9 10 ohms. at 20% RH. This paper was then extrusion coated with 0.4 mil of polyethylene on each side of the paper base. This resulted in a surface resistance greater than 1 1O ohms, the same as plain polyethylene film. In the same series being tested, the effect of various degrees of electrical conductants coated on the internal paper stock were compared, and this was further compared to a conventional coating of antistatic material on the polyethylene surface.

Letter A below was the internally antistatic treated material. Letter B used an untreated paper base, but the same antistatic material as in Letter A as a surface coating on one side of the polyethylene paper combination. Letter C used a carbon black loaded stock as the internal sheet. Component surface resistances in ohms at 20% RH. were as follows:

Untreated Compari- A B C son Paper base alone 7X10 9X10 7X10" 1 l0 Polyethylene surface 1X10 1Xl0 1X10 1X10 These polyethylene-paper combinations were then tested by running in contact with phenolic rollers at various speeds and the strength of the electrostatic field thus generated was measured. Electrostatic field measurements were as follows in Table I.

At web speeds up to 500 ft. per minute, no difliculties in conveyance resulted and no visible discharge was seen when the special internally treated polyethylene paper combination Letter A above was used. Letters B also eliminated conveyance difliculties, and C was likewise satisfactory in both respects.

EXAMPLE 2 A 15% aqueous solution of a sodium salt of naphthalene sulfonic acid, was used as a tub size to treat a 25- lb. per 1000 sq. ft. paper stock to obtain a coating of 1 pound per 1000 sq. ft. The resulting surface resistance was 5 10 ohrns at 20% RH. This paper stockwas B then extrusion coated with 0.4 mil of polyethylene on each side of the paper base, With a resulting surface resistance of greater than 1 10 ohms. The finished material was tested by running it in contact with phenolic rollers at various speeds and the strength of the electrostatic field thus generated was measured, as indicated as follows in Table II.

Table II ELECTROSTATIC FIELD VOL'IS Speed, ft/min. Untreated Tarnol Comparisons Treatment 'lam0l is the sodium salt of naphthalene sulfonic acid.

In comparing Table II with Table I, it is shown that the static reduction is directly related to electrical resistance of the treated paper before polyethylene coating, and the more conductive it is, the greater the static protection.

Polyethylene is a preferred coating composition, but other polymeric materials may be used including the poly-alpha-olefins having 2-10 carbon atoms for example polyethylene and polypropylene, and organic synthetic thermoplastic materials such as polyesters, polyamides, polyacetals, polycarbonates, cellulose derivatives, such as cellulose esters and ethers, and the like.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereina'bove and as defined in the appended claims.

We claim:

1. A photographic paper comprising a paper base, an antistatic agent incorporated therein and on at least one side of the paper base, a synthetic polymer coating free of antistatic agent selected from the class consisting of poly-a-olefins, polyesters, polyamides, polyacetals, polycarbonates, cellulose esters and cellulose ethers and a photographic emulsion on the coated paper.

2. A photographic paper comprising a paper base, an antistatic agent incorporated therein, a polyethylene coating free of antistatic :agent on at least one side of the paper base, and a photographic emulsion on the coated paper.

3. A photographic paper comprising a paper base, an antistatic agent incorporated therein, a polyethylene coating free of antistatic agent on at least one side of the paper base, and a photographic emulsion on the coated paper adhered to the polyethylene coating.

4. A photographic paper comprising a paper base, an antistatic agent incorporated therein, a polypropylene coating free of antistatic agent on at least one side of the paper base and a photographic emulsion on the coated paper.

5. A photographic paper comprising a paper base, an antistatic agent incorporated therein, a polypropylene coating free of antistatic agent on at least one side of the paper base and a photographic emulsion on'the coated paper adhered to the polypropylene coating.

6. A photographic paper comprising a paper base, an antistatic agent incorporated therein, a polyethylene coating on both sides of the paper base and a photographic emulsion adhered to the polyethylene coating.

7. A photographic paper comprising a paper base having sodium sulfate incorporated therein as an antistatic agent, a polyethylene coating on both sides of the paper base and a photographic emulsion adhered to the polyethylene coating.

I (References on following page) References Cited by the Examiner UNITED STATES PATENTS Minsk et a1. 9685 Kline et a1. 162138 Bell et a]. 9687 Laakso et a1 9685 Dalton 162138 Whitman 162-138 6 FOREIGN PATENTS 587,456 2/ 1960 Belgium. 853,186 11/1960 Great Britain.

5 NORMAN G. TORCHIN, Primary Examiner.

LOUISE P. QUAST, Examiner.

J. T. BROWN, T. I. HOFFMAN, R. H. SMITH,

Assistant Examiners. 

1. A PHOTOGRAPHIC PAPER COMPRISING A PAPER BASE, AN ANTISTATIC AGENT INCORPORATED THEREIN AND ON AT LEAST ONE SIDE OF THE PAPER BASE, A SYNTHETIC POLYMER COATING FREE OF ANTISTATIC AGENT SELECTED FROM THE CLASS CONSISTING OF POLY-A-OLEFINS, POLYESTERS, POLYAMIDES, POLYACETALS, POLYCARBONATES, CELLULOSE ESTERS AND CELLULOSE ETHERS AND A PHOTOGRAPHIC EMULSION ON THE COATED PAPER. 